Formation of patterned media by selective anodic removal followed by targeted trench backfill

ABSTRACT

A method is disclosed for defining discrete magnetic and non-magnetic regions on the magnetic film layer of a storage media substrate. The method applies anodic oxidation of a cobalt-containing magnetic film layer to remove cobalt, followed by controlled deposition of a non-magnetic matrix into the regions where the cobalt has been removed. Deposition may either be electrodeposition, collimated vacuum deposition, or other methods depending upon the composition of the non-magnetic matrix being deposited. The method may be performed in a single electrochemical cell.

FIELD

This disclosure relates generally to the formation of patterned media ordiscrete track media for use in storage media. Specifically, thisdisclosure relates to the deposition of a non-magnetic matrix to formpatterned media or discrete track media.

BACKGROUND

Bit patterned media (BPM) and discrete track media (DTR) are becomingmore popular media for storage because of their inherent abilities tostore more data in a smaller area. The goal of BPM and DTR and otherpatterned media is to increase bit density. However, manufacturingmethods for BPM and DTR are complicated, expensive and inconsistent.

BPM media are typically formed by using lithography to define thepattern on the media substrate. Once the pattern is defined, thetranslation of the pattern to the media substrate is typically anadditive or subtractive process. An additive process, e.g.,electrodeposition and lift-off, requires steps of creating a resistpattern and then depositing a magnetic film layer. In contrast, thesubtractive process begins with the deposition of a magnetic film layerfollowed by resist patterning. The resist pattern may serve as an etchmask such that the surrounding magnetic film may be removed by ionmilling, reactive ion etching (RIE), wet chemical etching or otherprocesses. An issue with these types of etching is that they are notvery selective in defining magnetic and non-magnetic regions on themagnetic film layer. As a result, etching does not always result inconsistently higher bit densities.

Other methods have been reported with varying results. For example,focused ion beams (FIB) poisoned with gallium (Ga⁺) have been used inorder to created discrete magnetic islands (also referred to as “dots”or “bits”) smaller than 70 nm in diameter. However, magnetic film layermodification using FIB is not readily scalable to mass production.

What is therefore needed is a way to define discrete magnetic andnon-magnetic regions on a magnetic film layer that is both efficient andscalable to mass production.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of this disclosure are illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which likereferences indicate similar elements, and in which:

FIG. 1 is a perspective view of individual bit cells in a bit-patternedmedia.

FIG. 2 is an exemplary flow diagram illustrating the steps of anembodiment of the disclosure.

FIG. 3 is an image illustrating an embodiment.

FIG. 4 is an image illustrating an embodiment.

FIG. 5 is a cross-sectional view of a medium undergoing a methodembodiment.

FIG. 6 is an exemplary chart illustrating an embodiment.

FIG. 7 is an exemplary chart illustrating an embodiment.

FIG. 8 is an exemplary chart illustrating an embodiment.

FIG. 9 is an exemplary flow diagram illustrating the steps of anembodiment.

FIG. 10 is a cross-sectional view of a medium undergoing a methodembodiment.

SUMMARY OF THE DISCLOSURE

An embodiment includes a method for forming patterned media byselectively oxidizing a cobalt-containing magnetic film layer on amedium substrate, then depositing or “backfilling” a non-magnetic matrixin the regions of the cobalt-containing magnetic film layer where thecobalt was removed. An embodiment includes an electrochemical cell forselectively oxidizing a cobalt-containing magnetic film layer to removecobalt, and then backfilling the removed cobalt with a non-magneticmatrix.

DETAILED DESCRIPTION

A method for forming patterned media is disclosed herein. The patternedmedium is formed by selective anodic oxidation of a cobalt-containingmagnetic film layer on the medium substrate, then depositing orbackfilling a non-magnetic matrix in the regions of thecobalt-containing magnetic film layer where cobalt was removed. By wayof example, FIG. 1 depicts an exemplary storage medium 104 comprising anarray of magnetic dots 108 in a magnetic film layer. Each magnetic dot108 is capable of storing a single bit of information. A typicalmagnetic film layer may be comprised of cobalt (Co) and platinum (Pt).

FIG. 2 is a flowchart illustrating the steps of an exemplaryoxidation-reduction method in which the removal of cobalt from the mediasubstrate and backfilled with a non-magnetic matrix in a singleelectrochemical cell, or “one-pot” method. As will be explained furtherbelow, the progress of the reaction may be attenuated by lowering thecurrent applied to the single electrochemical cell. In FIG. 2, theelectrochemical cell contains an electrolyte solution comprised ofH₂PtCl₆, H₃BO₃ and NH₄Cl. The PtCl₆ ⁻² species in the electrolytesolution may act as the oxidizing agent while at the same time providingthe Pt species for the non-magnetic matrix. In an embodiment, the pHlevel of the electrolyte solution is 5.0.

In block 201 of FIG. 2, a CoPt magnetic film is sputter or otherwisedeposited onto a seed layer of a media substrate. The seed layer may bea ruthenium (Ru) seed layer or other equivalent layer. In block 203 ofFIG. 2, Co is selectively removed from the magnetic film layer byselective anodic oxidation by lowering the current or potential in theelectrolyte solution. This step may also be referred to herein as“anodic removal” or “AR.” AR will leave tracks or bits of 1.0-5.0 nm inthe magnetic layer where CoPt is left behind, and grooves or trenches inthe magnetic layer where Co has been selectively removed. FIG. 3 is anexample of a transmission electron microscopy (“TEM”) image of DTR mediain which Co has been selectively removed from the magnetic film layer,leaving behind a 2.0-3.0 nm groove. One skilled in the art willappreciate that when viewed through a scanning electron microscope(“SEM”), a top-down view of DTR media which has had Co selectivelyremoved using AR will show less dense, more porous, labyrinth-likemicrostructures in the areas exposed to AR as compared to the areas notexposed to AR.

One skilled in the art will appreciate that removing Co from aCoPt-containing magnetic film layer may leave Pt remaining in thegrooves or trenches. This may be confirmed by observation with across-sectional TEM and nano-energy dispersive X-ray spectrometer(“nano-EDX”), in which the grooves or trenches may show a strong Ptsignal as compared to areas not exposed to AR. One will appreciate thatas a result of the remaining Pt, the interface between the CoPt bits andthe exposed Pt layer may form a galvanic cell that can enhance thecorrosion rate of the remaining CoPt between anodic oxidation and thefollowing rinsing or drying steps. However, because the method of FIG. 2occurs in a single electrochemical cell, the opportunity for CoPtcorrosion is significantly reduced. In block 205 of FIG. 2, the Pt insolution will be electrodeposited into the grooves left from the removedCo from block 203 of FIG. 2. FIG. 4 is a TEM image of DTR media in whichan overabundance (˜20 nm) of Pt has been electrodeposited into thegrooves. One will appreciate that the excess Pt may be stripped in orderto provide a substantially flat media surface.

One skilled in the art will also appreciate that removing Co from aCoPt-containing magnetic film layer using an oxidation process may leavea non-conductive oxidized film in the groove, as shown in FIG. 3. Thismay inhibit electrodeposition, since it is generally preferred that thesurface upon which electrodeposition takes place be generallyconductive. In order to encourage electrodeposition of Pt into thegrooves, the medium may require pretreatment, such as pre-wet cleaning,chemical activation, cathodic reduction or other methods. Pretreatmentmay ensure that the surface of the grooves is generally conductive andthe surface of the tracks or bits is non-conductive.

FIG. 5 is a cross-sectional view of a medium undergoing the method ofFIG. 2. In block 501 the media substrate may comprised of a photoresist(“PR”) layer, a magnetic layer and one or more underlayers beneath themagnetic layer. The media substrate may be descummed in block 503 inorder to remove foreign contaminants or residue. In block 505 of FIG. 5,the media substrate undergoes AR as described in block 203 of FIG. 2. Inblock 507 of FIG. 5, the trench or groove left from the AR process maybe backfilled with the electrodeposition of Pt, NiPt (“NiP”) or otherplatinum-containing compounds. In block 509 of FIG. 5, the mediasubstrate may be stripped to form a substantially flat surface. In block511 of FIG. 5, the carbon overcoat (“COC”) may be deposited onto themedia substrate.

As mentioned previously, the progress of the electrolyte reaction may becontrolled by lowering the electric potential (measured in volts (V) vs.saturated calomel electrode (SCE)). One skilled in the art willappreciate that the voltages applied in the examples disclosed hereinare merely exemplary and that other ranges are possible withoutdeparting from this disclosure or the scope of the appended claims. Forexample, FIG. 6 is a chart of a rotating disc electrode (RDE)voltammetry study run in H₂PtCl₆ solution at a range from pH 2.0 to pH5.0, and illustrates that Pt may be deposited at potentials morenegative than −0.4 V vs. SCE (shown as −400.0 mV in FIG. 4). As shown,FIG. 7 illustrates that selective anodic removal of Co from CoPt in anH₂PtCl₆ solution having a pH of 5.0 occurs at a peak potential ofE_(p)=0.018 V vs. SCE. Pt oxidation can occur at E_(p)=0.45 V vs. SCE.One will appreciate that the rate of reaction may also be controlled byvarying potential. In an embodiment, the method illustrated in FIG. 2may be completed in 20 seconds. During the first 10 seconds at +0.3 Vvs. SCE, selective removal of Co from the CoPt magnetic layer occurs byanodic oxidation. During the second 10 seconds, when potential isstepped to −0.4 V vs. SCE, Pt⁴⁺ is reduced to Pt and electrodepositedinto the trenches left by the removed Co. This rate of reaction isillustrated in the chart of FIG. 8.

One will appreciate that electrodeposition may be used to backfill othernon-magnetic matrices containing other metals besides Pt. For example, ametal or alloy containing Pt, Ru, Ni, P, Cu, NiPt, CuNi, etc., may beelectro-deposited into the trenches formed by the anodic removal of Coin block 203 of FIG. 2. electrodeposition may be more desirable thanother deposition methods, such as vacuum deposition, since it mayprovide an even deposition of certain non-magnetic matrices withoutdisturbing the tracks or bits left from the oxidation step. As a result,a low cost media fabrication process is provided because the need forpost backfill lift-off or other CMP processes is obviated.

Even though electrodeposition may be a preferred method for backfillingthe magnetic layer, one will appreciate that vacuum deposition methodsmay be used as well. For example, if a media manufacturer wants to use ametal or alloy containing Cr, Ta, NiTa, Ni, Ti and/or Cu, or use othernon-magnetic matrices, it may employ alternative methods withoutdeparting from the scope of the appended claims or this disclosure. FIG.3 illustrates a method using collimated vacuum deposition of Cr. In themethod of FIG. 3, the anodic oxidation step may not occur in the samereaction vessel, or “one-pot” as the deposition step because it requiresdifferent conditions.

In block 901 of FIG. 9, a CoPt magnetic film is sputter deposited onto aseed layer, which may be a Ru seed layer or other equivalent layer. Inblock 903 of FIG. 9, Co is selectively removed from the magnetic filmlayer by selective anodic oxidation to leave tracks or bits in themagnetic layer where CoPt is left behind, and grooves or trenches in themagnetic layer where Co has been selectively removed. In block 905 ofFIG. 9, Cr is deposited into the trenches using collimated vacuumdeposition techniques.

FIG. 10 is a cross-sectional view of a medium undergoing the method ofFIG. 9. FIG. 10 is similar to FIG. 5, except that Cr is deposited usingcollimated vacuum deposition rather than electrodeposition. In block1001, the media substrate may comprised of a photoresist (“PR”) layer, amagnetic layer and one or more underlayers beneath the magnetic layer.The media substrate may be descummed in block 1003 in order to removeforeign contaminants or residue. In block 1005 of FIG. 10, the mediasubstrate undergoes AR as described in block 903 of FIG. 9. In 1007 ofFIG. 10, the trench or groove left from the AR process may be backfilledwith the collimated vacuum deposition of Cr. In block 1009 of FIG. 10,the media substrate may be stripped to form a substantially flatsurface. In block 1011 of FIG. 10, the carbon overcoat (“COC”) may bedeposited onto the media substrate.

One will appreciate that the methods describe herein disclose methodsfor controlled deposition into a trench formed by anodic oxidation of acobalt-containing magnetic film layer. Because the deposition iscontrolled, little to no planarization of the magnetic film layer isrequired following deposition. This offers a significant advantage overmilled (IBE) patterned media which typically has a trench depth of about20 nm.

According to an embodiment, a result of one or more of the methodsdescribed above is a cobalt-containing magnetic film layer overlaying amedium substrate, the cobalt-containing magnetic film layer containing aplurality of magnetic portions separated from each other by anonmagnetic matrix. One will appreciate that the magnetic film layerdoes not have to be directly deposited upon or in contact with themedium substrate, and the magnetic film layer may be separated from theunderlying medium substrate by one or more interlayers. Using one ormore of the methods described above, the nonmagnetic matrix may comprisean electrodeposited metal selected from the group consisting ofplatinum, ruthenium, nickel and copper. In addition, the nonmagneticmatrix may comprise a vacuum deposited metal selected from the groupconsisting of chromium, tantalum and nickel.

One will appreciate that in the description above and throughout,numerous specific details are set forth in order to provide a thoroughunderstanding. It will be evident, however, to one of ordinary skill inthe art, that an embodiment may be practiced without these specificdetails. In other instances, well-known structures and devices are shownin block diagram form to facilitate explanation. The description of thepreferred embodiments is not intended to limit the scope of the claimsappended hereto. Further, in the methods disclosed herein, various stepsare disclosed illustrating some of the functions. One will appreciatethat these steps are merely exemplary and are not meant to be limitingin any way. Other steps and functions may be contemplated withoutdeparting from this disclosure or the scope of the appended claims.

What is claimed is:
 1. A method for forming a pattern on a substratecomprising: depositing a cobalt-containing magnetic film layer onto thesubstrate; selectively removing cobalt from the cobalt-containingmagnetic film layer; and depositing a non-magnetic matrix in the regionsof the cobalt-containing magnetic film layer from where cobalt wasselectively removed, wherein selectively removing cobalt and depositinga non-magnetic matrix are both performed in a single electrochemicalcell using the same electrolyte composition.
 2. The method of claim 1,further comprising patterning a resist on the top surface of thedeposited cobalt-containing magnetic film layer such that the patternedresist forms a mask on the top surface of the cobalt-containing magneticfilm layer.
 3. The method of claim 1, wherein the non-magnetic matrixcomprises platinum.
 4. The method of claim 1, wherein selectivelyremoving cobalt comprises applying anodic removal/oxidation.
 5. Themethod of claim 1, wherein depositing a non-magnetic matrix compriseselectrodeposition.
 6. The method of claim 1, wherein the depositednon-magnetic matrix comprises a metal or alloy selected from the groupconsisting of platinum, ruthenium, nickel, phosphorus and copper.
 7. Themethod of claim 1, wherein depositing non-magnetic matrix comprisesvacuum deposition.
 8. The method of claim 7, wherein the depositednon-magnetic matrix comprises a metal selected from the group consistingof chromium, tantalum, titanium, nickel and copper.
 9. The method ofclaim 1, wherein selectively removing cobalt from the cobalt containingmagnetic film results in the formation of a plurality of magneticislands.
 10. The method of claim 1, wherein selectively removing cobaltfrom the cobalt-containing magnetic film results in the formation of aplurality of magnetic tracks.
 11. A method for forming a pattern on asubstrate comprising: depositing a cobalt-containing magnetic film layeronto the substrate; selectively removing cobalt from thecobalt-containing magnetic film layer; and depositing a non-magneticmatrix in the regions of the cobalt-containing magnetic film layer fromwhere cobalt was selectively removed wherein selectively removing cobaltand depositing a non-magnetic matrix are both performed in anelectrolyte solution containing H₂PtCl₆, H₃BO₃ and NH₄Cl.